At the end of this module, you will be able to:
- Describe the purpose of the Yankee dryer coating
- Describe how the coating affects the drying and creping processes
- List common Yankee dryer coating ingredients
- Describe yankee coating application
The following key questions are answered in this module:
What are the components of Yankee dryer coatings?
Adhesives, release agents, and modifiers are the three main classes of coating chemicals.
What are adhesives?
Adhesives are poylmers that cross-link on the dryer and provide the base adhesion to stick and hold the sheet to the dryer surface.
What are modifiers?
Modifiers added to the coating formulation to change some aspect of the adhesion. They can be used to increase the adhesion, soften the coating, improve the re-wettability of the coating, or control the amount of coating that builds on the dryer. Polyvinyl alcohol (PVOH) is a common modifier.
How is the coating applied?
A sprayboom under the Yankee dryer between the cleaning doctor and pressure roll sprays the coating mixture onto the dryer surface.
What are some indications of coating problems?
Coating problems can cause streaks or bare spots on the Yankee surface, uneven reel build, uneven creping blade wear, sheet wrinkling, uneven draws, or loose/tight sheet edges.
Below is a transcript of the video sample provided for this module:
Coating chemicals are sprayed directly onto the dryer surface by the Yankee Sprayboom after the Creping Doctor. The purpose of the coating is to hold or stick the sheet to the Yankee in order to ensure uniform crepe, uniform drying, and overall high sheet quality. The creping blade removes the sheet from the dryer's surface, but the point of separation is actually under the sheet, in the layer of coating. This brings up two important points, first that the creping blade does not contact the drier surface, rather it rides in the coating. Because the creping blade is usually made of a material that is much harder than the Yankee dryer, this prevents severe wear of the dryer. Secondly, not all of the coating is removed by the creping blade. Some coating remains on the dryer surface at all times.
Use the additional resources and links below to learn more about this topic: